Just use
plt.axvline(2.8, 0,0.17)
And the same for the other line
Here instead of 0.17 you can put the maxima of your distribution using some variable such as maxx = max(data) or something similar. 2.8 is the position on the x-axis. Oh remember that the y-value has to be in between 0 and 1 where 1 is the top of the plot. You can rescale your values accordingly. Another obvious option is simply
plt.plot([2.8, 2.8], [0, max(data)])